In the prior art, a communications system is usually provided with two receivers: a main receiver and a diversity receiver. Interface circuits of antennas of the receivers are shown in FIG. 1. A common contact c0 of a main connector is connected to the main receiver, a normally-closed contact c1 is connected to a main antenna, and a normally-open contact c2 is connected to an external antenna. That is, according to a specific requirement of an actual application scenario, the main receiver may connect to the main antenna or the external antenna, and the diversity receiver can only connect to a diversity antenna. Performance of the external antenna is higher than that of the main antenna, and the performance of the main antenna is higher than that of the diversity antenna.
To ensure MIMO (multiple-input multiple-output) performance of a system, a performance difference between a main receiver and a diversity receiver is usually not expected to be excessively great. However, when the main receiver is connected to an external antenna and the diversity receiver is connected to a diversity antenna, because there is a great performance difference between the external antenna and the diversity antenna, there is also a great performance difference between the main receiver and the diversity receiver, which further affects the MIMO performance of the system.